BRACKISHWATER ECOLOGY ZOOL 22034_UPK EPA
Lagoons & Estuaries cover around 158,000 ha in Sri Lanka
Point Point Pedro, Dondra
Bay Arugam Bay, San Fransisco Bay
Lagoon Koggala, Kalametiya
FRESH WATER MARINE WATER Estuary
What is the definition of an estuary? The tidal effect perspective A sediment perspective A Biological perspective Most common definition Recent overall definition
Tidal effect perspective: An estuary is an inlet of the sea, reaching into the river valley as far as the upper limit of the tidal rise. Usually being divisible into three sectors: a) a marine lower estuary: in free connection with the open sea b) a middle estuary: subject to strong fresh and salt water mixing c) an upper or fluvial estuary: characterised by fresh water but subject to daily tidal action. Dionne (1963)
A sediment perspective: The seaward portion of a drowned river valley system which receives sediment from both fluvial and marine sources and which contains faces influenced by tide, wave and fluvial processes. Dalrymple et al.(1992)
A biological perspective: An estuary is a semi-enclosed coastal body of water that extends to the effective limit of tide influence,... and can sustain euryhaline biological species for either part or the whole of their life cycle. Perillo (1995)
Most common: An estuary is a semi-enclosed coastal body of water which has free connection to the open sea and within which sea water is measurably diluted with fresh water derived from land drainage. Cameron & Pritchard (1963)
Most satisfactory overall definition from an oceanographic / hydrographic perspective (modification of Pritchard's to include tides). An estuary is a semi-enclosed coastal body of water which has free connection to the open sea, extending into the river as far as the limit of tidal influence, and within which sea water is measurably diluted with fresh water derived from land drainage. Dyer, (1997)
Summary (Important factors) Rivers (strong salinity gradients) Tides (influence mixing & salt intrusion) Sediments (marine and fluvial) Biota Waves Geology Classification depends on your perspective!
Why are Estuaries Important? Fertile waters Organic material Juvenile species Navigational access to inland areas Center of man's development Sedimentation Dispersion of pollutants Need to assess man's environmental impact. (e.g. pollutants, deforestation, dredging, dams, removal of river water)
Aquaculture Ornamental fish/ Fishery Wild life Eco tourism Timber/ Food etc. Lime stone/ clay mining Sea weed collection Salt production Sewage and garbage disposal Research and Education
How are estuaries formed? Result of changes in sea level During the Pleistocene Ice Age (approx. 1.6 mybp) sea level was 100m below present levels. Since the Flandrian transgression sea levels have risen steadily by about 1m / century!
Classification of Estuaries Descriptive classifications by tides Classification based on water balance Classification by topography Classification on salinity structure
Descriptive classifications by tides 1) Tidal Range (Davies, 1964): - Microtidal <2m - Mesotidal 2-4m - Macrotidal 4-6m - Hypertidal >6m
2) Equality between convergence and friction, (Nichols & Biggs, 1985): - Hypersynchronous estuaries Convergence > Friction Tidal amplitude increases towards head of the estuary. - Synchronous estuaries Convergence = Friction Tidal amplitude remains constant towards head of the estuary. - Hyposynchronous estuaries Convergence < Friction Tidal amplitude decreases towards the head of estuary.
Classification based on water balance 1. Positive Estuaries fresh water input from ground water, rivers, rainfall exceeds evaporation (net flow of fresh water into ocean); most estuaries are this type. 2. Negative estuaries evaporation exceeds fresh water input. This can happen in tropical lagoons with little fresh water input (salinity >35 ppt). Hypersaline lagoons. Eg. Puttalam 3. Neutral estuaries fresh water input = evaporation. This system is not that practicable, because a single estuary could go from 1 to 3 to 2 in a year.
Classification by topography Drowned river valley (Coastal Plain Estuaries): (Pritchard 1952) - formation: Flandrian transgression; sedimentation<inundation - depth: fairly shallow (<30m, river valley unchanged) - shape: triangular in cross-section - width/depth => large - sediments: recent sediment; mud becoming sandy towards mouth - occurrence: temperate latitudes - river flow: high river flow, low sedimentation. e.g. Thames, Trincomalee, Mersey.
Low sediment discharge + high tidal range = drowned river valley About 70,000 years ago the sea level in this area rose 60 metres, flooding the Karuah River valley and forming the estuary of Port Stephens, NSW, Australia.
Bar-built estuaries: - formation: like drowned river valleys but sedimentation higher than inundation. - features: bar across mouth formed by wave driven currents. associated with depositional coasts, restricted tidal range but strong tidal currents at the mouth. extensive lagoons. - depth: very shallow, typically <10m. - shape: irregular - often large lagoon. - width/depth => very large - sediments: thick sediments, often protrudes seawards (Vellar estuary 300m in 36 yrs) - occurrence: tropical areas with active deposition - river flow: large and seasonal, high sedimentation. e.g. Veller estuary (India); Puttalam and Negambo estuaries
A bar-built estuary
Estuaries formed by tectonic activity - formation: faulting, land slides and volcanic eruptions - features: Very deep - depth: v. deep - shape: triangular in cross-section - width/depth => small - sediments: rocky floors - occurrence: high latitudes. e.g. San Francisco Bay (USA)
River delta Estuary formation: Deposition of sand and mud - features: Number of small islands - depth: v. shallow - shape: varies - width/depth => Large - sediments: muddy floors, sediment deposition mainly at the mouth of the estuary. - occurrence: Nile River estuary Mekong River High sediment discharge + low tidal range = deltas
Fjords: - formation: erosion by Pleistocene ice sheet (glaciations) - features: bars & shallow sills at entrance; sills restrict tidal ventilation (sill depth 4-140m); often anoxic. - depth: v. deep (up to 800m) - shape: rectangular in cross-section - width/depth => small (10:1) - sediments: rocky floors, thin veneers of sediment, deposition mainly at the head of the estuary. - occurrence: high latitudes. e.g. Loch Etive (Scotland), Sogne Fjord (Norway) Milfered Sound (New Zealand)
Classification based on salinity Stratified Estuary structure Partially stratified Estuary Well mixed Estuary
Fresh water from River Fresh water from River Sea water wedge
Physical characteristics of estuaries The General Pattern of Salinity Distribution Oxygen ph Temperature Light Tides Sedimentation
Factors affecting productivity in Estuaries Size and Depth Turbidity Rainfall / River Flow Velocity Vertical Relief Tidal Amplitude Sub surface counter current Pollution
Biological features of an estuary PLANKTON Phytoplankton Zooplankton Nekton Benthos Other estuarine associated animals (and plants)
Estuarine Plankton Autochthonous Populations (Holoplankton) Temporary Autochthonous Populations (Meroplankton) Allochthonous Populations
Estuarine phytoplankton Taxonomic composition Diatoms Dinoflagellates Chlorophytes Chrysophytes Cryptophytes size classification Net plankton: > 20 mm Nannoplankton: < 20 mm Picoplankton: < 2 mm
Estuarine zooplankton Macrozooplankton: net-collectable zooplankton (> 200 mm) Holoplankton spend entire life in plankton Can comprise 80 90 % of numbers in plankton 0 70 ppt broad salinity tolerance (euryhaline) Meroplankton(> 200 m m) spend part of life in plankton
Copepods - These tiny crustaceans the size of a rice grain are estimated to be most numerous multicellular animals on earth. These are the "insects of the sea" and are a source of food for many other zooplankton and fish Krills - These zooplankton are important source of food for many marine/ brackish water mammals and seabirds. They are especially well known in the Antarctic where they are an important part of the food web Crab zoea - The larvae of many bottomdwelling invertebrates like crabs, starfish, mussels, clams, and lobsters all begin as larvae in the plankton before they settle on the bottom and become the more familiar adult creatures
Life cycle of a crab
Microzooplankton: not collectable in nets, filterable (< 200 m m) Size is main classification criterion Many are too small for plankton nets (which are as small as 80 mm) May be underestimated in zooplankton surveys (twice as abundant as the net zooplankton)
Estuarine Fauna (Nekton and other associated organisms) Factors that influence the distribution of animals, Tidal changes Salinity changes Physical and chemical factors Nature of the substratum Grazing and predation Fishing
Reasons for a fewer species in brackish water fauna 1. Rigorous nature of the physical environment 2. The short life span of the estuary Low level of spatial diversity
Estuarine Nekton Fish and invertebrates that swim, use and migrate between different habitats Autochthonous Populations Allochthonous Populations From River From Sea
Organisms found in Negambo Estuary TYPE FISH SHRIMP MOLLUSCS Autochthonous organisms Allochthonous From Sea Allochthonous From Rivers 38 01 05 80 06 03 07 01 -
Life cycle of shrimp POST LARVA PROTOZOEA JUVENILE MYSIS NAUPLIUS POST LARVA ADULT EGGS ESTUARY OCEAN
Major groups of animals found in and around the estuary Protozoans Coelenterates Annelids Nematodes Mollusks Arthropods Fishes Amphibians Mammals
INTERACTIONS AMONG ORGANISMS IN AN ESTUARINE ECOSYSTEM
TROPHIC LEVELS IN AN ESTUARINE ECOSYSTEM